The present invention relates to an air compressor, and in particular, it relates to an air compressor suitable for controlling a cooling fan through an inverter.
Requirements for lowering electric power consumption and noises of an air compressor are increasing. In addition to a variable speed control provided by means of an inverter within a main body of the compressor, developments are also made to a variable speed control provided by means of the inverter for a fan motor to be used in a heat exchanger. With an inverter control of the fan motor, since a rotation speed of the fan motor can be increased or decreased depending upon an increase/decrease of a load needed, the advantage of achieving the lowering of electric power consumption and of noises can be obtained.
An example of applying an inverter control to the cooling fan of the air compressor is provided by a screw compressor which is shown in Patent Document 1 identified below. The screw compressor of Patent Document 1 comprises a main compressor body having a pair of male/female screw rotors, an air-cooled type cooler for compressor lubrication oil, an air-cooled type cooler for compressed air, a cooling fan for supplying cooling air to the main body of the compressor and the air-cooled type coolers mentioned above, an inverter for controlling the rotation speed of the cooling fan, a first sensor for detecting temperature of the lubrication oil, a second sensor for detecting temperature of a suction air, and a cooling fan controller.
The control of the cooling fan controller has a memory portion for memorizing the setup temperature of the lubrication oil and the setup temperature of the suction air, and a calculation portion for calculating a control signal for increasing the rotation speed of the cooling fan mentioned above when a detected value of temperature of the lubrication oil from the first sensor becomes higher than the setup temperature, which is memorized in the memory portion, or for calculating a control signal for increasing the rotation speed of the cooling fan when a detected value of temperature of the suction air from the second sensor becomes higher than the setup temperature of the suction air, which is memorized in the memory portion mentioned above.